The invention relates to a steering device for motor vehicles with a steering shaft.
Steering devices for motor vehicles are frequently implemented in two parts, one slidable into the other such that in the event of a frontal collision the steering device does not endanger the driver whereby the steering device upon an impact of the body onto the steering wheel yields and the impact energy is absorbed. In the known devices conventionally the slidable steering shaft tube, which receives the control wheel-side steering shaft, is disposed in a casing which is clamped with respect to the motor vehicle chassis by machine screw fastening in predetermined position. The machine screw fastening is herein implemented such that upon impact the steering wheel-side shaft end with the machine screwed casing bracket in the axial direction, in the clamped state is displaceable by a specific path. The impact energy is correspondingly absorbed by the clamping. In order to make the energy absorption more uniform in the event of impact, additional energy absorption elements had been disposed between the longitudinally slidable shaft part and the chassis of the motor vehicle. An energy absorption element, which is implemented as a sheet metal tongue which can be torn away, is for example known from GB 1,390,889.
One disadvantage of the known crash system for steering columns comprises that, on the one hand, the break-free force could not be defined over wide ranges substantially independently of the energy absorption force. The absorption behavior could also not be reproducibly preset.
The object of the present invention is to propose a crash system for a steering column configuration, which eliminates the disadvantages of the prior art. The object comprises in particular realizing a crash system for steering columns which permits a defined break-free force and a defined energy absorption under reproducible behavior. In addition, the configuration is to be simple to mount and economical in production.
According to the invention the configuration is implemented such that in the event of an impact the break-free force is decoupled from the energy absorption force upon sliding of the steering shaft.
Thus, in the event of a crash the clamping is to be released immediately, for the purpose of which serves a so-called break-free element in order to dissipate the impact energy after the breaking free of the clamping substantially onto an energy absorption element. Therewith is attained that the energy absorption over the defined displacement path is substantially no longer affected by undefined clamping forces and the absorption effect is specifically presettable through the implementation of the absorption element.
For an embodiment of the break-free element, for this purpose in the region of the clamping securement where the high clamping forces between casing bracket and the stationary chassis part occur, the facing portions pressed onto one another through the clamping are slightly inclined with respect to the sliding direction, i.e. disposed at a specific wedge angle such that already with a short displacement path the original clamping is immediately reduced thereby that the two wedge face parts move apart depending on the angular slope. In this way, in the case of an impact the clamping is already broken after a displacement of a few tenths mm and the further displacement is no longer determined by undefined clamping forces. The casing bracket, which fixes the steering shaft tube, is connected with the chassis via a tear-away strip. The implementation of this tear-away strip now determines essentially the degree and the [time] course of the energy absorption behavior. Through appropriate dimensioning of this tear-away flap the energy absorption behavior can be laid out correspondingly optimally gently for the driver.
A further preferred embodiment comprises that in the region of the compressed slide facing elevations are disposed on both sides of the facing, which are staying each other over a short path distance wherewith the slide facing is developed substantially in the short contact zones of the elevations and in the case of displacement, i.e. in the event of a breaking-free, the one elevation slides already after a short path distance, for example of a few millimeters, from the other elevation and thus generates the desired breaking free in the event of a crash. A further especially simple, preferred embodiment of a break-free element comprises that at least on a subregion of the clamped facing parts these opposing clamping faces are [stair]-stepped such that the clamping force is reduced after a short displacement path.
An especially cost-effective and space-saving steering column configuration with crash system for the energy absorption is obtained thereby that the steering shaft is supported in a guide box which, in turn, is fixedly connected with a retaining bracket, comprises laterally flange-like slide faces which, for example, are clamped tightly on the motor vehicle chassis by being machine screwed. The clamping is implemented such that in the event of a crash the steering shaft can be yieldingly displaced for example by several centimeters with the bracket. The energy absorption element is connected, on the one hand, stationarily with the chassis and, on the other hand, connected where the energy absorption takes place via the bracket with the steering shaft. The absorption element is implemented preferably as a sheet metal part with tear-away flap, which, developed, for example, in the form of a yoke as a tear frame, is mounted between the bracket flange and the chassis. This embodiment has the great advantage that the attachment of the configuration on the chassis is possible using only two attachment means, preferably two machine screws. This simplifies the implementation considerably and also permits a rapid mounting which has a positive effect on the total cost. The tightening torque of the machine screws are herein advantageously in the range from 15 to 35 Nm. This highly simple implementation of the configuration and, in particular the feasibility of securing the entire configuration with only two attachment machine screws without separate bracket guidance, permits also in simple application cases the use without the previously described special break-free elements. But in this case the defined separation between break-free force and energy absorption is less unique, but in exchange, the configuration is in this case realizable especially cost-effectively.